Thickness control apparatus for rolling mill

ABSTRACT

A thickness control apparatus for a rolling mill in which the output thickness of a moving web or strip is changed by changing the set value of the thickness of the rolling material from a specific point, and said thickness control apparatus is characterized in that the thickness of the rolling material is changed at the first stand, and the tension of the web or strip is controlled in the rest of the stands.

United States Patent Morooka et al.

[451 Apr. 17, 1973 THICKNESS CONTROL APPARATUS FOR ROLLING MILL Inventors:

Assignee:

Filed:

Appl. No.:

Yasuo Morooka; Masaya Tanuma; Mikihiko Onari, all of Hitachi, Japan Hitachi, Ltd., Tokyo, Japan Mar. 16, 1971 Foreign Application Priority Data Mar. 16, 1970 Japan ..45/2l512 US. Cl.....

Int. Cl.

Field of Search ..72/ 6-1 2 MOVING SIG GAP CAL- COEF MEMORY [56] References Cited UNITED STATES PATENTS 3,618,348 ll/l97l Arimura et al. ..72/7 R26,996 12/1970 Beadle et al ..-72/7 3,53 l ,96] 10/1970 Dunn .72/8 3,603,124 9/197l Arimura et al. ..72/8

Primary ExaminerMilton S. Mehr Att0rneyCraig, Antonelli, Steward & Hill I ABSTRACT A thickness control apparatus for a rolling mill in which the output thickness of a moving web or strip is changed by changing the set value of the thickness of the rolling material from a specific point, and said thickness control apparatus is characterized in that the thickness of the rolling material is changed at the first stand, and the tension of the web or strip is controlled in the rest of the stands.

19 Claims, 2 Drawing Figures MOVING SIG PAIENIED W I 7 SHEET 2 or 2 F I G 2 THICKNESS CHANGING POINT D m q 5 8 50 NN m NE 4 HS T. T% T UT m P 3 m mw G o $N m NN 2 A wH HC T 0 I I I O V mmmzxoik TIME (sec) \1 D m S 5 88 D m mm a I H I H E T M T% UT WP U0 3 O 2 T m m I NG N m 0 H Tm w mo 0 o o wWUZXQTC.

OUTPUT THICKNESS THICKNESS 0.45 CHANGING POINT 0 II wmmzxoik Imrn) TIME IsecI G D W N m %m M M C H T W 5 F T H M m H S T 8 I P E 4E TF N M U0 K O m T H T 3 T W. m

G 2 G N m m G N N A A H H C I C S S S S Em E N m w IB 0 m H H T T: m4 m0 0 O mmmzxoik THICKNESS CONTROL APPARATUS FOR ROLLING MILL BACKGROUND OF THE INVENTION The present invention relates to automatic thickness control systems for changing the set value of the output thickness of a moving web or strip in the rolling mill.

The multi-stand rolling mill, in the prior art, provides from a rolling material a web or strip having a specific thickness. With an increasing demand for more varied rolling products in recent years, the rolling mill has been required to have greater capacity and higher efficiency and to be capable of providing a wide range of products.

In the prior art, however, time-consuming procedures are required for changing the parameters set for the rolling mill when a different rolling product is desired. To change the set values, therefore, the rolling efficiency must be sacrificed. Furthermore, once rolling has started, it must be continued to the end of the material being rolled. This makes it difficult to obtain a specific length of web or strip during one operation.

SUMMARY OF THE INVENTION In view of the foregoing, a general object of this invention is to provide a thickness control apparatus capable of accurately and quickly changing the thickness of a rolling web or strip.

Briefly, according to the present invention, the coefficient affecting the output thickness of a moving web or strip produced by changing independently the roll gaps in the individual stands and the coefficient affecting the tension thereof in each stand are found by measurement or logical equations, the roll gap variation in each stand is calculated according to said coefficients, thus permitting the output thickness of the web or strip and the tension thereof in each stand to be set at the desired values, and the roll gap of each stand is changed each time the thickness changing point reaches the respective stand.

More specifically, the change of the final output thickness is determined almost entirely by the roll gap change in the first stand, the roll gaps of the other stands being changed mainly by changing the tension thereof. The roll gap of the first stand is controlled according to the set value of the final output thickness, and the other roll gaps are controlled according to the set value of the tension adapted to the final output thickness.

Thus, according to the invention, a rolling mill is provided which is capable of continuously producing a product with different thicknesses.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram illustrating an apparatus embodying this invention; and

FIGS. 2 (a) through 2(e) are graphic representations illustrating the shapes of a rolling web or strip in the vicinity of the thickness changing point in each stand shown in FIG. I.

DESCRIPTION OF THE PREFERRED EMBODIMENT i 22 Asa,

where n designates the number of stands. When n is 5 in the rolling mill,

Ahflh =alAS a AS a AS a,,AS a AS 2 The changing value (Ah/h on the uncoiler side of the 1" stand can be obtained by summing the products of the changing value AS,- of the roll gap of the i" stand and the coefficient b affecting the tension in the j" stand. For example,

fl i z bbwgs-(jzl 2 n-1 n) tbi i=1 II I i a From equation (3), the changing values in the five stands are given as m/ In tI l I2 2 ia a m 4 I5 5 m/ n2 ZI 1 22 2 23 3 24 4 zs s ha/ ba aI i 32 2 aa a 34 4 as s AI b AS, b AS b AS b AS b AS (7) Ar /1,, b AS, b AS b As b As, b .-,AS, (8)

In the ordinary rolling mill where a constant tension control device is used on the uncoiler side as well as on the coiler side, the tension changing value (Ar /r on the uncoiler side of the first stand and the tension changing value (Ar /r5 on the coiler side of the fifth stand are nearly equal to zero.

The thickness changing method of this invention will be described below based on equations (2) and (4) through (8 Substituting the final output thickness changing value for Ah, of equation (2), and the tension changing value for t,, of equations (4) through (8), and solving the simultaneous equations (2) and (4) through (8) with five unknowns, the roll gap changing values A8,,

A8 A8 A5 AS of the individual stands can be deter mined as set values changed for the final output thickness and tension. To find the roll gap changing value from the above equations, it is necessary to obtain coefficients. Tables 1 and 2 show the necessary coefiicients obtained according to measurements on a five-stand rolling mill.

TABLE 1 Ratio of Final Output Thickness Changing Values Ist 2nd 3rd 4th 5th stand stand stand stand stand (AhF/liF) 0.1565 0.0273 ().OOI9 '(J.OOO() 0.0184

Note: The roll gaps of individual stands are changed independently by 1 mm. The width of the web or strip produced is 930 mm and the thickness is changed from 2.0 to 0.4mm.

TABLE 2 Ratio of Uncoilcr Side Tensions 1st 2nd 3rd 4th 5th stand stand stand stand stand m/ m) O O O O r /1 0.380 1.027 0.074 0.007 0.00l ba/ m) 0. I82 ().030 0.094 0.480 I as/ bs) Note: The roll gaps of individual stands are changed independently by 1 mm. The width of the web or strip produced is 930 mm and the thickness is changed from 2.0 to 0.4 mm.

Table 1 shows the ratio of the final output thickness changing values under the condition that the roll gaps of individual stands are changedindependently from each other. In the above example, the roll gap changing value in each stand is 1 mm, or in other words, the roll gap changing value provides the coefficient affecting the final output thickness of each stand. For example, the coefficient a affecting the final output thickness in the first stand is 0.1565. While Table 2 shows the ratio of the uncoiler side tension under the condition that the roll gaps of individual stands are changed independently. In this case, the roll gap changing value of each station is l mm. Hence, this roll gap indicates the coefficient b affecting the uncoiler side tension in the 1 stand. For example, the coefficient bag affecting the uncoiler side tension in the third stand due to the roll gap change in the second stand is 0.084.

In Table 2, the values b,, are provided at the intersection of the i stand column and the (At /t ).row. if the coefficients can be obtained in the manner as shown in Tables 1 and 2, then an ideal roll gap changing value in each station can be found through the foregoing equaequations are simplified; namely, equation (1) is rewritten Ahp/hF =a,AS Similarly, equation (3) is Equations (2) and (5) through (8) can be expressed as AhF/hF=a,AS, 2y AIIIZ/IDZ 2i l 22 2 (5 ba/ &3 3l l as a Al /l b AS (7 ba/ o5 5l 1 as s (8 in order to change the final output thickness by Ah, so as to obtain the specified value of tension in each stand, the roll gap of each stand must satisfy the following equations.

In the above equations, Ar /r Ai /1 AI /t Ar,,,Jt,,,, are determined to be suitable according to the changing value of the final output thickness. These values can be found from measurement and logical equations. When the change Ah, of the final output thickness is small, Ar /r Ar /2 AIM/1M and Ar /1,,

can be reduced to zero. In this case, equations (9) through l 3) are rewritten as follows.

From equations 14) through 18), it is apparent that the roll gap is changed so that the final output thickness is changed by changing the first stand roll gap, and the tension change caused by said roll gap changed is absorbed by another roll gap change.

To change the roll gap based on the above equations, it is necessary to change the roll gap sequentially from the stand reaching the thickness changing point. Thus, a speedy and accuratev thickness change can be realized.

The invention will be more specifically described with reference to the accompanying drawings.

Referring to FIG. 1, there is shown an embodiment of this invention applied to a five-stand rolling mill, which includes stands 1 through 5 of the rolling mill, a thickness detector 10, roll screw down devices 1 1 through 15, motors 21 through 25 for driving the roll screw down devices 11 through 15, speed controllers 31 through 35 for the individual stands, speed detectors.

41 through 45 for the individual stands, a material de- -tector 50, thickness changing point detectors 6] through for detecting the presence of the thickness changing point as it reaches each stand and for instructing the roll gap change for the corresponding stand, gate circuits 71 through 75, moving signal calculators 81 through 85 for calculating the moving signal A mi thereby operating the roll screw down devices according to the roll gap changing value A S,, gap calculators for calculating the roll gap changing value A8,, gap caling the value of the coefficient memory in the next control. The reference 130 represents a tension changing value memory for storing the tension changing value adapted to the changing value of the final output thickness for the purpose of obtaining the tension thereof in each stand, conforming to the final thickness set value. Elements 200 through 202 are input terminals, and element 203 is an input terminal for receiving an uncoiler side tension input for each stand.

A thickness value which may most frequently be required in the rolling mill, or a thickness value which is suitable for use as a standard is chosen from among popular thickness values. Such a thickness value is used as a standard, and the roll gap value of each stand corresponding to the standard thickness is stored in the roll down controller 100. The roll gap is set according to this standard thickness, and the roll speed is set by the speed controllers (31 through 35) of each stand. Then, rolling starts.

When the tip end of the rolling material reaches the first stand, the material detector 50 located on the input side of the first stand starts generating an output signal. By means of this signal, the detected value V of the first stand speed detector 41 is supplied to the first stand thickness changing point detector 61. The thickness changing point detector 61 of the first stand calculates the length of the rolling material passing through the first stand according to the roll speed value V When the length thereof reaches a specific value set via the input terminal 200, namely when the thickness changing point reaches the first stand, the detector 61 starts generating an output signal. While, on the other hand, the difference AhF between the final output thickness value hF in the existing schedule and the value hF in the following schedule is applied to the gap calculator 91 via input terminal 202. To the gap calculators 91 through 95, necessary coefficients are applied from the coefficient correcting device 110, and also the tension changing values adapted to the final output thickness Ah, are applied from the tension changing value memory 130. The gap calculators 91 through 95 calculate gaps according to equations (9) through l3 and supply the roll gap changing values AS, to the moving signal calculators 81 through 85.

It is assumed that the tension of each stand is not 7 opened. By this means, Am is supplied to the motor 21 to operate the roll screw down device 11, thereby changing the first stand roll gap by AS By means of the output signal of the thickness changing point detector, the second stand roll speed value V is delivered from the speed detector 42 to the second stand thickness changing point detector 62. In the same manner, when the thickness changing point reaches the i'" stand, the thickness changing point detector generates an output signal. By this means, Am is supplied to the motor to operate the roll screw down device, thus changing the roll gap of the i" stand by A5,. In other words, the thickness change is finally completed at the instant the thickness changing point passes through the fifth stand.

According to the embodiment as illustrated in FIG. 1, the feed of the material into the first stand is detected by the material detector 50, the material with a specific thickness is rolled to a length being set via the input terminal 200, and the material thickness is changed automatically to the value set for the next stand. Namely, by supplying the input terminal 200 with the value set for the next stand. Namely, by supplying the input terminal 200 with the value of length to each thickness changing point in succession, the thickness is automatically changed when the material is fed to the set length.

Instead of the thickness changing point detector 61 and material detector 50, other means may be employed wherein the thickness changing signal is applied to the thickness changing point detector 62 and the gate circuit 71 is opened whereby the thickness can be changed to a desired value.

According to this invention, the coefficient at which the final output thickness is changed and the coefficient at which the tension in each stand is changed with change of the gap of each stand are obtained, while on the other hand, the difference between the standard final output thickness and the desired thickness, and also the tension in each station adapted to the thickness are supplied thereto whereby the roll gap value of each station is obtained and thus the rolling thickness is quickly changed.

The accuracy of the rolling mill is increased in the following manner. The final thickness is detected by the thickness detector 10, the coefficient a,A affecting the final output thickness at the change of the roll gap of the first stand is calculated by the coefficient correcting device according to said detected final thickness, and the subsequent change in thickness is accomplished by using the coefficient a A. The coefficient a A is obtained by the following equation.

a,A=(hF-hF"/hF")(l/AS,) 19 where hF is the final output thickness after thickness change,

hF is the final output thickness before-thicknes change, and

AS is thefirst stand roll gap changing value.

The value a,A obtained by equation (19 includes an external disturbance. To smooth the value a A, the following equation is used. I

a',A=a,+cr(a,A-a' where a,A is the coefiicient after smoothing,

a, is the coefficient adapted and corrected in the previous schedule,

a is a constant, and

a,A is the coefficient obtained by equation 19).

Similarly, from equations (10) through (13), the values b b and h are found by the use of the coefficient correcting device, to change the value of the coefficient memory. Instead of the operation using the detected value supplied from the thickness detector 10, the tension value of each stand is given to the input terminal 203 whereby At, (i=2-5) is calculated. In this case, the values h h b. and b are not changed.

The standard tension values i t t and t are independently set and not changed. The value AS ('F2-5) is applied from each of the gap calculators 92 through 95 to the coefficient correcting device. By the above arrangement and procedures, the accuracy of a rolling mill can further be increased.

FIGS. 2(a) through 2(e) show the shapes of the rolling material in the vicinity of the thickness changing point in the thickness changing control according to this invention. It is apparent from the figure that the material is rolled perfectly to the desired thickness except for the area in the vicinity of the thickness changing point. In short, the invention makes it possible to realize a continuous thickness change of the rolling material with a high accuracy and at a high speed, and thus, to reduce the time involved in the rolling operation and to minimize the rolling efficiency.

While we have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible. of numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to coverall such changes and modifications as are obvious to one of ordinary skill in the art.

We claim:

l. A thickness control apparatus for a multi-stand rolling mill in which the thickness of a moving web is changed from a first value to a second value at a certain specific point on the moving web, comprising detecting means for detecting a thickness changing point at each roll stand, gap calculator means for calculating the roll gap changing values for the respective stands according to a coefficient affecting a final output thickness due to the roll gap change in each stand and also a coefficient affecting the tension in each stand due to said roll gap change, the coefficient affecting the final output thickness and the coefficient affecting the tension in each stand being provided by independently changing the roll gaps in the individual stands, and thickness control means for changing the roll gap at each roll stand according to the roll gap changing value provided from said gap calculator means.

2. A thickness control apparatus as defined in claim 1, wherein said detecting means includes speed detecting means at each roll stand and first means at the first roll standresponsive to an input signal indicating the length of web to be rolled at a standard thickness and the output of said speed detecting means at the first roll stand for generating an output for effecting actuation of said thickness control means at the first roll stand by said gap calculator means.

. 3. A. thickness control apparatus as defined in claim 2, wherein said detecting means includes second means at each roll stand subsequent to said first roll stand responsive to the output of the detecting means at the previous roll stand and the speed detecting means of the respective roll standfor effecting actuation of said thickness control means of the respective roll standby said gap calculator means when said specific point on the moving web reaches that roll stand.

4. A thickness control apparatus for a multi-stand rolling mill in which the thickness of a moving web is changed from a first value to a second value at a specific point on the moving web, comprising detecting means for detecting the thickness changing point at each roll stand,

thickness control means for controlling the roll gap at each roll stand in response to respective gap control signals,

roll down control means for providing standard gap control signals for the respective roll stands,

gap calculator means responsive to an input gap changing value signal for generating changing value gap control signals including memory means for storing predetermined thickness and tension coefficient values for calculating said changing value gap control signals in accordance with said input gap changing value signal, the thickness and tension coefficient values being provided by changing the roll gap for the respective roll stands independently,

summation means for summing the respective standard gap control signals and changing value gap control signals to produce said gap control signals roll stand responsive to an input signal indicating the length of web to be rolled at a standard thickness and the output of said speed detecting means at the first roll stand for generating an output for effecting actuation of said thickness control means at the first roll stand by said gap calculator means.

6. A thickness control apparatus ad defined in claim 5, wherein said detecting means includes second means at each roll stand subsequent to said first roll stand responsive to the output of the detecting means at the previous roll stand and the speed detecting means of the respective roll stand for effectingactuation of said thickness control means of the respective roll standby said gap calculator means when said specific point on the moving web reaches that roll stand.

7. A thickness control apparatus as defined claim 6, including thickness detector means located at the output of the last roll stand for detecting the thicknessof said web, said gap calculator means further including coefi'icient correction means responsive to the output of said thickness detector means, said changing value gap control signals, and said input gap changing value for correcting the predetermined thickness and tension values stored in said memory means.

8. A thickness control apparatus as defined in claim 7, wherein said gap calculator means further includes tension changing value memory means for storing tension changing values adapted to the changing value of the final output thickness of said moving web.

9. A thickness control apparatus. as defined in claim 4, including thickness detector means located at the output of the last roll stand for detecting the thickness of said web, said gap calculator means further including coefficient correction means responsive to the output ofsaid thickness detector means, said changing value gap control signals, and said input gap changing value for correcting the predetermined thickness and tension values stored in said memory means.

10. A thickness control apparatus for a multi-stand rolling mill in which the thickness of a moving web is changed from a first value to a second value at a certain specific point on the moving web comprising roll speed detectors disposed at each of the individual stands, detector means for detecting the thickness changing point at each roll stand according to the roll speed detected by said roll speed detector, gap calculator means in which the first stand roll gap changing value is calculated by the coefficient affecting the final output thickness thereof due to the roll gap change in the first stand and the roll gap changing values in the stands subsequent to the first stand are calculated by using the roll gap changing value in the first stand and the coefficient affecting the uncoiler side tension in the stands subsequent to the first stand, and roll gap controller means for controlling the roll gaps of the stand in response to control from said thickness changing point detecting means according to the roll gap changing values provided from said gap calculator means.

11. A thickness control apparatus as defined in claim 10, including thickness detector means located at the output of the last roll stand for detecting the thickness of said web, said gap calculator means including memory means for storing predetermined thickness and tension coefficient values for each roll stand and coefficient. correction means responsive to the output of .said thickness detector means and the roll gap changing values for correcting said predetermined thickness and tension values stored in said memory means.

12. A thickness control apparatus as defined in claim 11, wherein said gap calculator means further includes tension changing value memory means for storing tension changing values adapted to the changing value of the final output thickness of said moving web.

13. A thickness control apparatus as defined in claim 1, wherein the gap calculator means and the thickness control means serve for changing the thickness of the moving web from the first value to the second value by substantially changing the roll gap of the first roll stand to provide for a substantial change in thickness of the web and for changing the roll gaps of the other roll stands to substantially control the tension of the web.

14. A thickness control apparatus as defined in claim 13, wherein the gap calculator means and the thickness control means change the roll gap of the first stand in accordance with a set value of the final output thickness of the web and change the roll gaps of the other stands in accordance with a set value of the tension adapted to the final output thickness of the web.

15. A thickness control apparatus as defined in claim 4, wherein the gap calculator means and the thickness control means serve for changing the thickness of the moving web from the first value to the second value by substantially changing the roll gap of the first roll stand to provide for a substantial change in thickness of the web and for changing the roll gaps of the other roll stands to substantially control the tension of the web.

16. A thickness control apparatus as defined in claim 12, wherein the gap calculator means calculates a roll gap changing value for each roll stand in accordance with the e uations A 2 2z A b2/ b2 21/ 22) A 1 where A h,/h; is the final output changing value,

A S, is the roll gap change value for the ith stand,

a, is the coefficient affecting the final output thickness for the ith stand,

A t /t is the tension changing value for the ith stand,

b is the coefficient affecting tension in the ith stand due to roll gap change in the first stand, and

b is the coefficient affecting tension in the ith stand due to roll gap change in the ith stand.

17. A thickness control apparatus as defined in claim 12, wherein the gap calculator means calculates a roll gap changing value for each roll stand in accordance with the equations where A h /h, is the final output changing value,

A S,- is the roll gap change value for the ith stand,

a, is the coefficient affecting the final output thickness for the ith stand,

b is the coefficient affecting tension in the ith stand due to roll gap change in the first stand, and

b is the coefficient affecting tension in the ith stand due to roll gap change in the ith stand.

18. A thickness control apparatus as defined in claim 12, wherein the coefficient correcting means corrects the predetermined thickness coefficient values in accordance with the equations where a A is the Corrected thickness coefficient value,

hF is the final output thickness after thickness change,

hF is the final output thickness before thickness change, and

AS 1 is the first stand roll gap changing value.

19. A thickness control apparatus as defined in claim 18, wherein the coefficient correcting means includes means for smoothing the corrected thickness coefficient value in accordance with the equation where a, A is the coefficient after smoothing,

a, is the coefficient adapted and corrected in the previous schedule, and 0' is a constant. 

1. A thickness control apparatus for a multi-stand rolling mill in which the thickness of a moving web is changed from a first value to a second value at a certain specific point on the moving web, comprising detecting means for detecting a thickness changing point at each roll stand, gap calculator means for calculating the roll gap changing values for the respective stands according to a coefficient affecting a final output thickness due to the roll gap change in each stand and also a coefficient affecting the tension in each stand due to said roll gap change, the coefficient affecting the final output thickness and the coefficient affecting the tension in each stand being provided by independently changing the roll gaps in the individual stands, and thickness control means for changing the roll gap at each roll stand according to the roll gap changing value provided from said gap calculator means.
 2. A thickness control apparatus as defined in claim 1, wherein said detecting means includes speed detecting means at each roll stand and first means at the first roll stand responsive to an input signal indicating the length of web to be rolled at a standard thickness and the output of said speed detecting means at the first roll stand for generating an output for effecting actuation of said thickness control means at the first roll stand by said gap calculator means.
 3. A thickness control apparatus as defined in claim 2, wherein said detecting means includes second means at each roll stand subsequent to said first roll stand responsive to the output of the detecting means at the previous roll stand and the speed detecting means of the respective roll stand for effecting actuation of said thickness control means of the respective roll stand by said gap calculator means when said specific point on the moving web reaches that roll stand.
 4. A thickness control apparatus for a multi-stand rolling mill in which the thickness of a moving web is changed from a first value to a second value at a specific point on the moving web, comprising: detecting means for detecting the thickness changing point at each roll stand, thickness control means for controlling the roll gap at each roll stand in response to respective gap control signals, roll down control means for providing standard gap control signals for the respective roll stands, gap calculator means responsive to an input gap changing value signal for generating changing value gap control signals including memory means for storing predetermined thickness and tension coefficient values for calculating said changing value gap control signals in accordance with said input gap changing value signal, the thickness and tension coefficient values being provided by changing the roll gap for the respective roll stands independently, summation means for summing the respective standard gap control signals and changing value gap control signals to produce said gap control signals applied to said thickness control means, and gate means associated with each roll stand and responsive to a respective output from said detecting means indicating presence of said changing point at the respective roll stand for applying the changing value gap control signal of the respective roll stand to said summation means.
 5. A thickness control apparatus as defined in claim 4, wherein said detecting means includes speed detecting means at each roll stand and first means at the first roll stand responsive to an input signal indicating the length of web to be rolled at a standard thickness and the output oF said speed detecting means at the first roll stand for generating an output for effecting actuation of said thickness control means at the first roll stand by said gap calculator means.
 6. A thickness control apparatus as defined in claim 5, wherein said detecting means includes second means at each roll stand subsequent to said first roll stand responsive to the output of the detecting means at the previous roll stand and the speed detecting means of the respective roll stand for effecting actuation of said thickness control means of the respective roll stand by said gap calculator means when said specific point on the moving web reaches that roll stand.
 7. A thickness control apparatus as defined in claim 6, including thickness detector means located at the output of the last roll stand for detecting the thickness of said web, said gap calculator means further including coefficient correction means responsive to the output of said thickness detector means, said changing value gap control signals, and said input gap changing value for correcting the predetermined thickness and tension values stored in said memory means.
 8. A thickness control apparatus as defined in claim 7, wherein said gap calculator means further includes tension changing value memory means for storing tension changing values adapted to the changing value of the final output thickness of said moving web.
 9. A thickness control apparatus as defined in claim 4, including thickness detector means located at the output of the last roll stand for detecting the thickness of said web, said gap calculator means further including coefficient correction means responsive to the output of said thickness detector means, said changing value gap control signals, and said input gap changing value for correcting the predetermined thickness and tension values stored in said memory means.
 10. A thickness control apparatus for a multi-stand rolling mill in which the thickness of a moving web is changed from a first value to a second value at a certain specific point on the moving web comprising roll speed detectors disposed at each of the individual stands, detector means for detecting the thickness changing point at each roll stand according to the roll speed detected by said roll speed detector, gap calculator means in which the first stand roll gap changing value is calculated by the coefficient affecting the final output thickness thereof due to the roll gap change in the first stand and the roll gap changing values in the stands subsequent to the first stand are calculated by using the roll gap changing value in the first stand and the coefficient affecting the uncoiler side tension in the stands subsequent to the first stand, and roll gap controller means for controlling the roll gaps of the stand in response to control from said thickness changing point detecting means according to the roll gap changing values provided from said gap calculator means.
 11. A thickness control apparatus as defined in claim 10, including thickness detector means located at the output of the last roll stand for detecting the thickness of said web, said gap calculator means including memory means for storing predetermined thickness and tension coefficient values for each roll stand and coefficient correction means responsive to the output of said thickness detector means and the roll gap changing values for correcting said predetermined thickness and tension values stored in said memory means.
 12. A thickness control apparatus as defined in claim 11, wherein said gap calculator means further includes tension changing value memory means for storing tension changing values adapted to the changing value of the final output thickness of said moving web.
 13. A thickness control apparatus as defined in claim 1, wherein the gap calculator means and the thickness control means serve for changing the thickness of the moving web from the first value to the second value by substantially changing the roll gap of the first rolL stand to provide for a substantial change in thickness of the web and for changing the roll gaps of the other roll stands to substantially control the tension of the web.
 14. A thickness control apparatus as defined in claim 13, wherein the gap calculator means and the thickness control means change the roll gap of the first stand in accordance with a set value of the final output thickness of the web and change the roll gaps of the other stands in accordance with a set value of the tension adapted to the final output thickness of the web.
 15. A thickness control apparatus as defined in claim 4, wherein the gap calculator means and the thickness control means serve for changing the thickness of the moving web from the first value to the second value by substantially changing the roll gap of the first roll stand to provide for a substantial change in thickness of the web and for changing the roll gaps of the other roll stands to substantially control the tension of the web.
 16. A thickness control apparatus as defined in claim 12, wherein the gap calculator means calculates a roll gap changing value for each roll stand in accordance with the equations Delta S1 1/a1 . Delta hf/hf Delta S2 1/b22 . Delta tb2/tb2 - (b21/b22) Delta S1 Delta S3 1/b33 . Delta tb3/tb3 - (b31/b33) Delta S1 Delta Si 1/bii . Delta tbi/tbi - (bi1/bii) Delta S1 where Delta hf/hf is the final output changing value, Delta Si is the roll gap change value for the ith stand, ai is the coefficient affecting the final output thickness for the ith stand, Delta tbi/tbi is the tension changing value for the ith stand, bi1 is the coefficient affecting tension in the ith stand due to roll gap change in the first stand, and bii is the coefficient affecting tension in the ith stand due to roll gap change in the ith stand.
 17. A thickness control apparatus as defined in claim 12, wherein the gap calculator means calculates a roll gap changing value for each roll stand in accordance with the equations Delta S1 1/a1 . Delta hf/hf Delta S2 - b21/b22 Delta S1 Delta S3 - b31/b33 Delta S1 Delta Si - bi1/bii Delta S1 where Delta hf/hf is the final output changing value, Delta Si is the roll gap change value for the ith stand, ai is the coefficient affecting the final output thickness for the ith stand, bi1 is the coefficient affecting tension in the ith stand due to roll gap change in the first stand, and bii is the coefficient affecting tension in the ith stand due to roll gap change in the ith stand.
 18. A thickness control apparatus as defined in claim 12, wherein the coefficient correcting means corrects the predetermined thickness coefficient values in accordance with the equations a1A hF - hF 1/hF 1 . 1/ Delta S1 where a1A is the corrected thickness coefficient value, hF is the final output thickness after thickness change, hF 1 is the final output thickness before thickness change, and Delta S1 is the first stand roll gap changing value.
 19. A thickness control apparatus as defined in claim 18, wherein the coefficient correcting means includes means for smoothing the corrected thicknesS coefficient value in accordance with the equation a''1A a''1 + sigma (a1A - a''1) where a''1 A is the coefficient after smoothing, a''1 is the coefficient adapted and corrected in the previous schedule, and sigma is a constant. 